A PM sensor (particulate matter sensor) for detecting the amount of particulate matter (hereinafter, referred to as PM) in an exhaust passage of an internal combustion engine is installed in a system, for instance, in Patent Document 1. The PM sensor includes an insulating substrate, and a pair of electrodes which is disposed on the insulating substrate and positioned apart from each other. If PM in exhaust gas deposit between the pair of the electrodes, conductive property between the electrodes changes with the amount of PM depositing, thereby changing resistance between the electrodes.
Moreover, in technique of Patent Document 1, the PM sensor is disposed downstream of a filter for trapping particulate matter. Therefore, the amount of PM depositing on the electrodes of the PM sensor is related to the amount of PM included in exhaust gas downstream of the filter for trapping particulate matter. In Patent Document 1, a defect of the filter for trapping particulate matter is detected based on the resistance between the electrodes of the PM sensor.